1. Field of the Invention
The present invention relates to a field emission image display utilizing field emission and to a method of driving the same.
2. Description of the Related Art
When the electric field at a surface of a metal or semiconductor is as large as 10.sup.9 V/m, electrons pass through the potential barrier because of the tunnel effect, thus emitting out in a vacuum at room temperatures. This phenomenon is called field emission. The cathode which emits electrons on the principle is referred to as a field emission cathode.
Recently, flat emission type field emission cathodes each formed of an array of micron-size field emission type cathodes have been able to be manufactured fully using semiconductor processing technology.
The structure of a field emission cathode called a Spindt type cathode is schematically shown in FIGS. 13(a) and 13(b).
FIG. 13(a) is a perspective view showing a FEC fabricated using the semiconductor fine-patterning technology. FIG. 13(b) is a cross-sectional view illustrating the FEC taken along the line A--A shown in FIG. 13(a).
Referring to FIGS. 13(a) and 13(b), cathode electrodes 102 of aluminum are formed on a cathode substrate 101 of glass by using vapor deposition. Cone emitters 105 are formed on the cathode electrode 102. A great number of gate electrodes 104 are formed over the cathode electrode 102 where the cone emitter 105 are not formed, via the insulating layer 103 of silicon dioxide (SiO.sub.2). The cone emitters 105 are respectively positioned in the openings formed in the gate electrode 104 and the insulating layer 103. That is, the tip of each cone emitter 105 is viewed in the opening formed in the gate electrode 104.
The pitch between the cone emitters 105 are fabricated to be less than 10 microns, using fine-patterning technology. Thus, several tens of thousands of FECs 105 to several hundreds of thousands of FECs 105 can be fabricated on a single substrate 101. The distance between the gate electrode 104 and the tip of the emitter 105 can be set in the order of submicrons. Hence the emitter 105 can emit electrons caused by the field emission by applying a small voltage of several ten volts between the gate electrode 104 and the cathode electrode 102.
The FEC can be made as a flat field emission cathode by forming an array of a great number of emitters 105 as shown in FIGS. 13(a) and 13(b). It has been proposed to apply the flat field emission cathode to flat color display panels. The cross-section of the color image display panel is partially shown in FIG. 14.
In FIG. 14, plural stripe cathode electrodes 102 are formed on the first substrate (cathode substrate) 101 of glass. Plural stripe gate electrodes 104 are arranged perpendicularly to the stripe-like cathode electrodes 102. The insulating layer 103 separates the cathode electrodes 102 from the gate electrodes 104. A great number of openings are respectively formed at the intersections where the cathode electrodes 102 and the gate electrodes 104 cross. The tip of each cone emitter 105 formed on the cathode electrode 102 within each opening directs upward.
The second substrate (anode substrate) 110 of glass is disposed so as to confront the first substrate 101. Metal anode electrodes 111 are formed nearly on the entire surface of the second substrate 110. Red fluorescent substance stripes 112 (R), green fluorescent substance stripes 113 (G), and blue fluorescent substance stripes 112 (B) are coated in one-to-one relationship at the corresponding positions of cathode electrodes 102 overlaying each anode electrode 111.
In the color image display with the above-mentioned structure, the stripe gate electrodes 104 are sequentially scanned one by one, and red, green and blue image data corresponding to one line selected with the gate electrode 104 are supplied to the stripe cathode electrodes 102. Thus, electrons of the amount corresponding to said image data are field-emitted from the emitter 105 disposed at the intersection of the gate electrode 104 and the cathode electrode 102 associated with the line in a driven state. The electrons impinge and glow the corresponding fluorescent substances 112 to 114. In such a manner, when all gates 104 are sequentially scanned and selectively driven, a full color image for one frame is displayed.
Generally, in the field emission image display, electrons emitted from the cone emitter 105 reach the anode electrode 111 with a beam angle of about 30. This means that electrons reach the anode electrode 111 with some divergence. This may cause electrons emitted from the emitter 105 to glow a adjacent different color fluorescent substances disposed on the anode substrate 111. Hence, there is the problem of blurring the displayed color image.
In order to solve such a problem, the present applicant proposed a field emission image display that can display blur-free color images by focusing electrons emitted from the emitter 105 (refer to Japanese Laid-open Patent publication (Tokkai-Hei) No. 8-298075).
FIG. 15 is a top view illustrating the field emission image display previously proposed.
Referring to FIG. 15, plural cathode electrodes 102 (depicted in chain lines) arranged on the first substrate are connected to cathode lead-out electrodes C.sub.1, C.sub.2, . . . , respectively.
Patchlike gate electrodes 120 corresponding to dots are arranged in two-dimensional matrix form on the cathode substrate 102 via an insulating layer (not shown). Two patchlike gate electrodes 120 are disposed on each cathode electrode 102 in the line direction perpendicular line direction. The emitters 105 (not shown) are arranged in an array pattern at the positions corresponding to the patchlike gate electrodes 120 on the cathode substrate 102.
The anode electrode 111 (shown in broken lines) is formed on the nearly entire surface of the second substrate (anode substrate) disposed corresponding to the cathode electrodes 102. R, G and B fluorescent substances are coated at the positions corresponding to the patchlike gate electrodes 120 on the anode electrode 111. In FIG. 15, symbols R, G and B labeled on each patchlike gate electrode 120 represent the luminous color of a fluorescent substance dot coated on the anode electrode 111.
As shown in FIG. 15, gate lead-out electrodes G are respectively connected to the patchlike gate electrodes arranged in the two-dimensional matrix. That is, the patchlike gate electrodes 120 corresponding to the odd-numbered G, B and R dots associated with the (i)-th line (column) are connected to the gate lead-out electrode GT.sub.(i)-1. The patchlike gate electrodes 120 corresponding to the even-numbered R, G, and B dots associated with the (i)-th line are connected to the gate lead-out electrode GT.sub.(i)-2.
The patchlike gate electrodes 120 corresponding to the odd-numbered G, B and R dots associated with the (i+1)-th line are connected to the gate lead-out electrode GT.sub.(i+1)-1. The patchlike gate electrodes 120 corresponding to the even-numbered R, G and B dots associated with the (i+1)-th line are connected to the gate lead-out electrode GT.sub.(i+1)-2. That is, two gate lead-out electrodes GT are alternately connected to patchlike gate electrodes 120 associated with each line.
A gate drive voltage is sequentially applied to the gate lead-out electrodes GT.sub.(1) to GT.sub.(n). When the gate lead-out electrode GT.sub.(i)-2, for example, is driven, the even-numbered R, G and B dots (hatched) associated with the (i)-th line are driven. An image can be displayed when the cathode lead-out electrodes 102, 102, . . . corresponding to the patchlike gate electrodes 120 supply the corresponding image data in agreement with the scanning timing of the gate electrodes. In such a condition, by setting the gate lead-out electrodes GT.sub.(i)-1, GT.sub.(i+1)-1, GT.sub.(i+1)-2 not driven at a low level, preferably to the ground potential, the neighbor patchlike gate electrodes 120 disposed around the patchlike gate electrode 120 (hatched) in a driven state are set to a low level potential. Thus, the electrons emitted from the patchlike gate electrode 120 in a driven state can reach the anode electrode in a focused beam state so that the blurred color can be eliminated.
In the field emission image display shown in FIG. 15, electrons emitted from the emitter 105 can reach a specific anode electrode with the beam focused so that the blurred color can be eliminated. Recently, there have been strong demands for image displays that can provide brighter, higher resolution images.
However, in the field emission image display shown in FIG. 15, the patchlike gate electrodes 120 are driven by means of two gate lead-out electrodes. Hence, the gate lead-out electrodes twice the number of actual display lines must be driven to display a full-color image for one frame by selectively driving all the display lines. For that reason, compared the case where the patchlike gate electrodes 120 associated with each line are driven by one gate lead-out electrode, the duty ratio becomes 1/2, so that it is difficult to realize a high brightness, high resolution image display.